Earlier today, Microsoft published the October 2017 Patch Tuesday, the company's monthly update train, addressing important security issues, but also some mundane bugfixes.
This month, the Patch Tuesday updates include fixes for 62 security bugs in applications such as the Windows OS, various Office offerings, Skype for Business, Internet Explorer, Microsoft Edge, and the Chackra Core browser engine.
Fix for Office Word zero-day included
Of all the bugs, the most important is a zero-day that was publicly disclosed and later used in attacks on live targets before Microsoft got around in releasing today's fixes.
The vulnerability (CVE-2017-11826) is a remote code execution (RCE) bug that affects Office Word, discovered by three Qihoo 360 security researchers.
Affected products include Microsoft Word 2007 and later releases, but also Word Automation Services and Microsoft Office Web Apps Server. Microsoft describes the issue as follows:
A remote code execution vulnerability exists in Microsoft Office software when the software fails to properly handle objects in memory. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the current user. If the current user is logged on with administrative user rights, an attacker could take control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
Exploitation of the vulnerability requires that a user open a specially crafted file with an affected version of Microsoft Office software. In an email attack scenario, an attacker could exploit the vulnerability by sending the specially crafted file to the user and convincing the user to open the file. In a web-based attack scenario, an attacker could host a website (or leverage a compromised website that accepts or hosts user-provided content) containing a specially crafted file designed to exploit the vulnerability. An attacker would have no way to force users to visit the website. Instead, an attacker would have to convince users to click a link, typically by way of an enticement in an email or instant message, and then convince them to open the specially crafted file.